Illuminated signs, such as are used, for example, on store fronts, or in some cases as signage in indoor public areas such as transit terminals and the like usually comprise a rectangular box containing some form of lighting, and a front face frame, which supports the sign panel itself. The sign information may be comprised in a variety of different ways, typically being a translucent panel of plastics material, but also including signs made of flexible synthetic fabrics, and other materials.
Usually, the face frame is hinged on the front of the box, so that it can be swung up and down for replacement of lamps and the like.
A variety of different designs have been proposed for the purpose. One form of illuminated sign box construction is shown in U.S. Pat. No. 3,863,372. The side and end walls of the box were all made of metal extrusions, of identical cross-section.
The contruction shown in that patent has been widely used, and has proved to be satisfactory in practice.
However, there are various areas where improvements can still be made. For example, in order to accommodate the needs of various different customers, it is desirable to offer sign boxes of different depths. Some may want a shallow box and others a much deeper box. Alternatively, some forms of illumination may require a deeper box than others.
In the past this could only be achieved by manufacturing the side and end wall extrusions in different widths.
However, it is obviously desirable that if possible the extrusion should be made modular so that with the same extrusion, simply by using one length, or two lengths attached together, a shallow and a deep sign box could be manufactured from the same extrusion.
In addition, it is desirable as far as possible to reduce the actual amount of metal in the extrusion simply for the sake of saving cost. However, in some circumstances, it is also desirable to reduce the amount of metal for other reasons such as ease of manufacture, shipping and fastening in place.
A further feature is the attachment of the back panel of the box. Usually in this type of illuminated sign box the back panel is made from thin sheet metal, and is attached to the rear edge of the four side walls of the box. Preferably, there should be a continuous sealed junction, at least along the top edge of the back panel, to keep out any moisture which may land on the top wall of the box. In the past, this was achieved, at least in the form of construction shown in the earlier patent, by a channel-like formation on the rear edge of the top wall, which was then swadged or squeezed onto the edge of the back panel. It is desirable, if possible, to eliminate this operation and to simplify the means of attachment, without losing the effectiveness of the seal.